Method of discontinuously sheathing heat-sensitive cables or the like



Apnl 1, 1958 E. EMMERICH 2,828,859

METHOD OF nxscouwmuousu SHEATHING HEAT-SENSITIVE CABLES OR THE LIKEFiled Oct. 7, 1954 METHOD OF DISCONTINUOUSLY SHEATHING HEAT-SENSITIVECABLES OR THE LIKE Ernst Emmerich, Koln-Bruck, Germany, assignor toSchloemann Aktiengesellschaft, Dusseldorf, Germany Application October7, 1954, Serial No. 460,961

Claims priority, application Germany November 20, 1953 2 Claims. (Cl.207-) In the sheathing of heat-sensitive cables or the like with heatedmaterials, for instance lead or aluminum, two requirements presentthemselves, which are almost incompatible. For reasons governingdeformation the temperature of the material to be dealt with must be ashigh as possible, as with increasing temperature the work required forthe deformation becomes less. For this reason a tates Patent '0tempertaure of about 250 C. is aimed at in the pressing of lead, whilstfor economically pressing aluminum temperatures of about from 450 to 530C. are aimed at.

On the other hand heat-sensitive cables, more particularly their outerinsulating layer, will not stand too intensive a heating, as they willotherwise be damaged. Insulating material based on synthetic substances,such as polyethylene and styrofiex are already heat-sensitive attemperatures of 150 and 75 C. respectively. The sensitiveness to heatis, of course, dependent on the duration of the action. Hence it ispossible to sheathe even relatively heat-sensitive cables or the likewith aluminum of fairly high temperatures, for instance of 530, when thepressure is applied very rapidly and small wall thicknesses are adopted,with which the amount of heat continuously given off can be conveyedaway to a sutficient extent. The cable will then run through the dangerzone so rapidly that the time will be insuflicient for any appreciabledamage to the cable. It is, of course assumed that all known means forcooling are properly applied, that more particularly the mandrel iscooled right to the point, that the matrix is cooled and that the cablesheathing being formed is cooled down immediately behind the matrix, forinstance by being sprayed with water.

The method referred to thus enables the production of sheathed cables tobe carried out only in such a length as can be carried out without theinterruption of a high pressing velocity. For sheathing, however,presses are preferably used in which the material operated on is placedin a container and is pressed out by a plunger. After the contents havebeen forced out of the container an interval must be interposed, duringwhich the press plunger is withdrawn and fresh material is introduced.When the container is very large, a relatively long cable can beproduced with great speed, but with a smaller container the length ofthe cable that can be produced diminishes in proportion to the volume ofthe container used. Large containers, however, require great pressingforces, so that the production of long cables with the aid of suchpresses is only possible when very large presses are used.

The invention has for its object, to produce discontinuously cablesheathings of any length, that is preferably with the aid of pressesoperating with a container and plunger, the arrangement being such thatseveral container charges can be pressed out one after the other,without damage due to heat to the cable insulation occurring at thestopping places referred to.

According to the invention this is effected by the pressing speed beingreduced before each stopping period grad- 7 2,828,859 Patented App 1,1958 ually in such a manner that the cable is exposed to the temperatureof the sheathing as it forms, which diminishes owing to the cooling,each time only as long as its material will stand it without beingendangered. Hence, shortly before the start or" the stopping period thepressing speed is gradually reduced. There is therefore an increase inthe length of time during which the heat ofthe sheathing in formation,of the mandrel and of the matrix acts on the section of cable as it runsthrough. At the same time, however, the temperature of theseheat-radiating materials decreases slowly, as mandrel, matrix and cablesheathing are continuously further cooled. Hence, whilst the period ofthe heat action on each cable section becomes longer, the eifectivetemperature drops at the same time and with it the amount of heatconveyed in unit time.

Through the employment of the method according to the invention itbecomes possible, even when using high pressing temperatures, to applylead and aluminum sheathing round heat-sensitive cables under pressurewith great pressing speeds and at the same time to interpose intervalsof several minutes for the purpose of adding fresh material. Forexample, it was found possible with a temperature of the aluminum chargeof 540 C. and a temperature of the recipient of the press of 530 C. topress round a cable of 20 mm., insulated with dry or impregnated paper,an aluminum sheath having a wall thickness of 1 mm. and to observestopping periods of' several minutes. No damage through heat action ofthe insulation was caused. The pressing velocity was found to bepreferably 10 cm./sec. This velocity was during one minute continuouslyreduced to zero, followed by a period of rest of several minutes.

Now, if a period of rest of any duration, for instance of one hour ormore, is to be interpolated, this is also possible, if the temperatureat the sheath-forming place be kept about constant at that which thecable will just stand. As the heat supply from the recipient cannot beinfluenced, this is effected by the expedient of throttling the coolingmedium supply in such a manner that the existing temperature which thecable is just capable of standing is not exceeded, but is substantiallymaintained; for the avoidance of excessively low temperatures is alsonecessary for enabling pressing to be resumed.

The regulation of the temperature is facilitated, if in the mandrelpoint and/ or the matrix one or more thermocouple elements be built in,which enable the temperature to be controlled. It is also possible tocause the supply of cooling medium to be directly automaticallyregulated by the thermocouple elements.

The attached diagram serves the purpose of elucidating the invention.

Let a indicate the cable to be sheathed. On the ordinate b thevelocities s are plotted, with which the individual cable sections 0,cl, 02 are drawn through the cable sheathing plates. The cable isnormally run quickly, that is to say, in the illustrated example withthe velocity s=l.

While the section 0 of the cable is running through the cable sheathingplace, a start is made with the reduction of the cable velocity. At thesame time the temperature starts to fall, being already substantiallyreduced at c1, whilst the section c2 is the one in which the cable isbrought to rest. Thus, at this place the place of junction between theexpression of two recipient charges is formed, which is usually referredto as bamboo ring or stopping place. On the ordinate d the temperaturesare plotted, which during operation prevail in the sheath formingregion. It is assumed that normal pressing proceeds at a temperatureround about 530. Now, if according to the invention the velocity withwhich the cable runs through the sheathing place is reduced within oneminute from 1 to 0, the temperature will also drop, as the supply of thecooling medium to the matrix, to the mandrel point and to the sprinklerremains unchanged. The temperature will therefore drop rapidly, so thatthe section (:1 of the cable will already be sheathed at a considerablylower temperature than the section 0. The sheathing takes far longer,however, than the sheathing of the section 0. 'When the velocity becomes0, the ternperature of 180 will be about reached. This temperature nolonger damages many insulating materials, even when it acts on thematerial for a considerable time, for instance for 1 hour. By throttlingthe supply of cooling medium it then becomes possible to cause thetemperature of 180 to be maintained for some time, as then the heatsupply from the recipient and the heat dissipation by the coolingdevices will balance one another. if the temperature of 180? bemaintained, it will be possible at any time to continue the pressing,Without appreciable damage to the cable through shrinkages due toexcessive cooling.

I claim:

1. A process for high temperature extrusion of successive billets toform a continuous metal sheath onto a cable having a heat-sensitivecovering without damaging the covering, particularly during replacementof billets, said process comprising the steps of feeding said cable at apredetermined linear speed, extruding a metal billet at an optimumtemperature considerably above the critical temperature at which saidcovering would be damaged by prolonged exposure to such optimumtemperature and at a speed related to said predetermined speed to formsaid sheath about said cable, cooling said sheath during said extrusionat a location immediately following the zone of extrusion at a constantrate to cool said sheath to a temperature just below that effectingdamage to said covering, continuing said cable feeding, extrusion andcooling at a substantially constant speed until the major portion ofsaid billet has been extruded, gradually and continuously reducing thespeed of extrusion and cable feeding to zero at a predetermined ratewhile continuing cooling at said constant rate which cooling due to thepredetermined rate of speed reduction operates to lower the temperatureof said sheath in the zone of extrusion to a temperature slightly belowthe critical temperature of said covering to prevent damage to saidcovering when the extrusion and cable feeding finally stop, said lowertemperature being sufliciently close to said critical temperature topermit etficient resumption of said extrusion operation, positioninganother billet for extrusion, resuming the cable feeding and extrusionoperation at said predetermined speedand optimum temperature whilecontinuing said constant cooling and repeating the process to provide asheathed cable of the required length.

2. A process as defined in claim 1, in which said predetermined linearspeed is approximately ten centimeters per second and in which saidspeed is reduced to zero through a period of approximate one minute.

References Cited in the file of this patent UNITED STATES PATENTS2,105,083'

